Shpongle

I have a question regarding varves. The common creationist response is that varves can form quickly. However, I was wondering if there are certain indicators within varve deposits that falsify this claim.

Why I ask, is I was doing some reading on varves and came across this regarding Green River varves from this site:

At basin margin, unit thickness is 30 cm and laminae number is as great as 1661. Alternatively, basin center is characterized by unit thickness of only 10 cm, and as few as 1238 laminae. Laminae thickness tends to fluctuate dramatically around the mean at the lake margin, but to a lesser degree at the lake center. Spectral analysis has not revealed any cyclicity that can be correlated to the 11-year sunspot cycle. This evidence supports a model of deposition where laminae represent calcite precipitation in response to episodic inflow. This process was likely the controlling factor of deposition for the entire lake, as no sunspot cycles were found in even the most distill samples. It is important that investigators establish that laminae are varves when trying to imply climatically induced depositional cycles. This is especially true in small lakes where inflow processes may be the controlling factor basin wide. (emphasis mine)

Now, I'm not going to pretend to understand everything in there (I'm no geologist), but they mention spectral analysis to correlate varve deposition with sunspot activity. Are there perhaps examples out there of varve depositions that have been correlated with sunspot activity (or something else, perhaps)?

ps418

Which, of course, is wrong by definition, since varves are annual deposits. It would be more correct to say that under some circumstances, thinly laminated deposits can form quickly.

Indeed there are. First, note that the abstact describes an analysis of one part of one member of the GRF -- a 10-30cm thick "middle unit of the Fossil Butte Member in southwest Wyoming." Meredith and Bucheim claim not to find any evidence for 11 year depositional cycle in this small section.

Second, its crucial to note that there are three seperate basins here, each of which has deposits assigned to the GRF. There is the huge Lake Giosute, and the unconnected and much smaller Fossil Lake, and Lake Uinta. Meredith and Bucheim are reporting results from Fossil Lake, not Lake Giosute or Lake Uinta. Orbital/seaonal cycles are well-established in Lake Giosute. 11yr cycles and much longer cycles are well-established for instance in the Tipton and Laney members (Fisher and Roberts, 1991; Ripepe et al, 1991) of the Lake Giosute portion of the GRF. Both ENSO cycles and putative sunspot cycles have been reported from the Lake Uinta deposits as well (Crowley et al, 1986), but as far as I know none have been described from fossil lake. So, nothing in Meredith and Buchheim appears to contradict the 'accepted wisdom.'

The illustration below, from Glenn Morton's article on the GRF, shows the layout of these basins.

http://www.glenn.morton.btinternet.c...enRiverMap.jpg

There is also very compelling sedimentary and radiometric evidence against 'catastrophic' formation of the GRF. One example I read about not too long ago are caddisfly/microbial stromatolites, which are something like insect reefs composed entirely of agglomerated caddisfly larval cases held together by (microbial?) carbonate. Leggitt and Cushman (2001) describe large, stromatolitic buildups, up to 9m tall and 40m in diameter and exposed along 70km of outcroup, from the base of the Laney Member of the Green River Formation. The buildups are arranged in a reef-like pattern along the northern margin of GRF in Wyoming (p. 377).

A unique aspect of these particular buildups is that they are characterized by couplets consisting of calcified, oriented caddisfly larval cases overlain by microbial laminae, overlain by more larval cases, etc. The Green River stromatolites were apparently repeatedly colonized by caddisfly larvae, perhaps because the surface microbes were a handy source of food. Leggitt and Cushman (2001) propose that that each caddisfly/microbial carbonate couplet represents a yearly pupation cycle, based upon observations of modern analogues, and the fact that most caddisfy species are univoltine (one life cycle per year). But whether they really represent yearly pupation cycles or not, they are fantastic evidence for the lake depostional model of the GRF, and fantastic evidence against 'catastrophist' models.

Tufa-encrusted logs and branches, which have been described from the fossil lake portion, again strongly supporting the lake depositional model.



A, Tufa encrusted branch. B, Surface texture of stromatolite growing on a tufa encrusted log. C, Stromatolite with rippled surface morphology growing on a tufa log. D, Bark impression on the reverse side of tufa encrusted log.

Loewen and Buchheim (1998) write:

Other sedimentary evidence, present in one or all three of the basins, includes dessication cracks, raindrop impressions, and vertebrate (bird) tracks in the proximal (i.e. shoreline) facies of the GRF. In the Fossil Lake portion of the GRF, several apparently in-situ bird (Presbyornis) nesting sites have been described, in the same Fossil Butte member, by Leggit, Buchheim, and Biaggi. I'll include a link to their article below. See Morton's article for refs on the bird tracks.

A final type of evidence bearing on the rate at which the GRF sediments accumulated is radiometric dating. The GRF contains quite a few ash horizons that, in principle, can be used to estimate depositional rates. And again, the results of such dating provide further evidence for the lake model and further evidence against the catastrophist model. For instance, here is the relevant part of the abstract from a recent set of 40Ar/39Ar determinations (Smith et al, 2003) from several tuffs in Lake Giosute (the one with the true varves). The results support both the validity of both the seaonal cycles (ie. varves), as well as a much longer precessional cycles, previously described, in the Tipton and Laney members:


Refs

Crowley, Kevin D., and Claude E. Cuchon and Jaeyoung Rhi, 1986. Climate Record in Varved Sediments of the Eocene Green River Formation. Journal of Geophysical Research, 918:8637-8647.

Fischer and Roberts, 1991. Cyclicity in the Green River Formation (Lacustrine Eocene) of Wyoming. Journal of Sedimentary Petrology 61, 1146-1154.

Morton, G., 2003. Creationist Misuse of the Green River Formation. Accessed 5/30/03.

Leggitt, V.L., Buchheim, H.P., and Biaggi, R.E., 1998. The stratigraphic setting of three Presbyornis nesting sites: Eocene Fossil Lake, Lincoln County Wyoming. National Park Service Paleontological: Technical Reports of the National Park Service.

Leggitt, V.L., and Cushman R.A.., 2001. Complex caddisfly-dominated bioherms from the Eocene Green River Formation. Sedimentary Geology. 145, pp. 377-396.

Loewen, Mark A., and H. Paul. Buchheim, 1998, Paleontology and paleoecology of the culminating phase of Eocene Fossil Lake, Fossil Butte National Monument, Wyoming. National Park Service Technical Report NPS/NRGRD/GRDTR-98/01:73-80.

Ripepe et al, 1991. ENSO and Sunspot Cycles in Varved Eocene Oil Shales from Image Analysis. Journal of Sedimentary Petrology 61, 1155-1163.

Smith et al, 2003. 40Ar/39Ar geochronology of the Eocene Green River Formation, Wyoming. Geological Society of America Bulletin: Vol. 115, No. 5, pp. 549–565.

Patrick

roxrkool

Ooooo... I really liked the insect reef stuff - never heard of it. That was cool!

BTW, some Creationists are suggesting the GRF is a post-flood deposit -- meaning the evidence for syn-flood *catastrophism* is weak. However, they still need the GRF laminae to have formed quickly, not seasonally, and these insect reefs are good ammunition.

Thanks for another great post, Patrick!!



Oh and "distill?" Looks like someone was downing a few too many when they reviewed that abstract.

Shpongle

Wow, thanks for the info ps418.

That stuff about the larval cases is very telling, and exactly the type of info I was looking for.